1. Field of the Invention
The present invention relates to a method of producing an electrostatic charge image developing toner and an apparatus for producing an electrostatic charge image developing toner, for use in development of electrostatic charge images in an electrophotographic copier, a laser beam printer, an electrostatic recording device, an electrostatic printing device etc. where images are formed by an electrophotographic method, an electrostatic recording method etc.
2. Description of the Related Art
In copiers for copying transcripts, printers for printing information outputted by computers including personal computers, and printers in facsimiles, an electrophotographic method or an electrostatic recording method has been widely used as a method of obtaining copied or recorded images. Typical examples of copiers and printers using the electrophotographic method or electrostatic recording method include electrophotographic copiers, laser beam printers, printers using liquid crystal arrays, and electrostatic printers. In the electrophotographic method or electrostatic recording method, an electrostatic latent image (electrostatically charged image) is formed by various means on an electrostatic image carrier such as an electrophotographic photoreceptor or an electrostatic recording medium, then the electrostatic latent image is developed by a developer, and the resulting toner image is transferred if necessary onto a transfer body such as paper, and fixed by heating, pressurization, or pressurization under heating or with an evaporated solvent to give a final toner image, while the residual toner onto the electrostatic image carrier, which is not transferred, is removed by cleaning means. These steps are repeatedly conducted to give a plurality of copies or prints.
Known methods of developing the electrostatic latent image include a wet developing method using a liquid developer having a fine toner dispersed in an electrically insulating liquid; and a dry developing method where a powdery toner having a colorant and if necessary a magnetic material etc. which are dispersed in a binder resin is used together with carrier particles, or a magnetic toner having a magnetic material dispersed in a binder resin is used without using carrier particles. Among these methods, the above-mentioned dry developing method using the powdery or magnetic toner is used mainly in recent years.
The magnetic or non-magnetic fine toner in a developer used in the dry developing method is produced in various manners. Examples of method of producing the toner powder in the developer include a pulverizing method, a spray drying method, a suspension polymerization method, and a microcapsulation method. The pulverizing method involves steps of preliminarily mixing a binder resin, a colorant, a charge control agent and other customary additives which are materials constituting the toner powder in an electrostatic developer, melt-kneading the mixture, cooling and pulverizing it into coarse powder and then finely pulverizing it and classifying the finely pulverized powder to give toner powder. The spray drying method involves steps of dispersing the constituent components in a binder resin solution and spray-drying the solution to give toner base particles. The suspension polymerization method involves steps of suspending and dispersing a monomer capable of forming a binder resin, a colorant and other additives in an aqueous solvent and polymerizing the mixture to give toner base particles. The microcapsulation method involves a step of incorporating predetermined materials into a core material and/or a shell material to give toner base particles. Among these methods, the production methods other than the pulverizing method are not practically widely used because the shape of the resulting toner base particles is nearly perfect sphere so that after transferring the toner onto a recording medium, there is a technical difficulty in cleaning the toner remaining on the image carrier and there is also an economical problem. Accordingly, the pulverizing method is generally used at present to obtain the electrostatic charge image developing toner.
In the method of producing the toner by the pulverizing method, materials constituting the toner are preliminarily mixed in a blender, melt-kneaded in a kneader to disperse uniformly the toner constituent materials in a binder resin, then cooled, pulverized and classified to give toner particles having desired particle-size distribution. The average particle diameter of the toner used in a developer for electrostatic charge images is usually 8 to 20 μm, but as the images with high quality are required in recent years, the toner having an average particle diameter of 6 to 12 μm is mainly used now. Then if necessary, a external additive is added to and mixed with the toner particles thus obtained, followed by removing aggregates by a sieve or the like, whereby the electrostatic charge image developing toner is obtained.
As the method of producing the toner by the pulverizing method, various methods have been proposed. As an example of typical methods using the pulverizing method, there is illustrated a closed circuit system wherein a pulverized starting material is pulverized by a pulverizer for pulverizing finely the starting materials, then the pulverized material is classified, and the whole of the classified coarse powder together with a pulverized starting material is fed again into the pulverizer and pulverized. In this closed circuit system, the whole of the classified coarse powder is fed again into the pulverizer. At this time, a change in the pulverization of the pulverizer appears as a change in the average particle diameter D50 of the pulverized material discharged from the pulverizer. Depending on this change in pulverization, the amount of the coarse powder fed again into the pulverizer is increased or decreased widely, thus causing a problem that excessive load to the pulverizer is given, or the particle-size distribution of toner powder obtained by classification changes. The change of the particle-size distribution of toner powder leads to unstable production of toners having constant particle-size distribution. To cope with such a problem, there are proposed a method wherein upon feeding the classified coarse powder to the pulverizer as returning powder, the returning powder is quantitatively supplied in amount of 5 times or less in the ratio than the amount of a pulverized starting material to be fed (see JP-A 3-209266).
This method is illustrated by reference to FIG. 4. Starting powder having a D50 of 300 to 500 μm is used, and this starting powder is fed in a predetermined supplying amount f1 from a pulverized stating material quantitative feeder 41 to a pulverizer 42 for pulverizing the starting materials finely, where the starting material is pulverized. The pulverized material is sent to a coarse-powder classifier 43 consisting of a rotating air classifier where coarse powder is classified and then returned to the pulverizer 42. Upon returning classified coarse powder to the pulverizer 42, the classified coarse powder is stored once in a returning-powder quantitative feeder 47 where the amount f2 of the returning powder fed from the returning-powder quantitative feeder 47 to the pulverizer 42 is regulated to be 5 times or less relative to the amount f1 of a pulverized starting material to be supplied. The returning-powder quantitative feeder 47 is provided with a weight detector. The particle diameter D50 of the classified and captured pulverized product is measured, while by the weight detecting function of the weight detector, the difference (Δw1) between the amount f3 of the returning powder fed from the rotating air classifier 43 to the returning-powder quantitative feeder 47 and the amount f2 of the powder fed from the returning-powder quantitative feeder 47 to the pulverizer is measured. When there is a change in D50 and Δw1, the optimum values of revolution number r1 of a rotating blade in the coarse-powder classifier and the amount f1 of the pulverized starting material to be supplied are calculated based on a predetermined formula, to correct the revolution number r1 of a rotating blade in the coarse-powder classifier and the amount f1 of the pulverized starting material to be supplied. This correction may be conducted by automatically measuring the particle diameter of the classified and captured pulverized product and the weight of the returning-powder quantitative feeder, and automatically regulating the revolving speed of the air classifier and the amount f1 of the supplied pulverized starting material by a computer. The pulverized material from which coarse powder was removed is sent to a cyclone 44 where the pulverized material from which coarse powder was removed is captured to give a pulverized product. Exhaust gas from the cyclone 44 is sent to a bug filter 45 where fine powder is captured, and the gas is discharged from a blower 46.
By this method, the particle diameter of the classified and captured pulverized product comes to be within a certain range, and the amount f2 of the powder fed from the returning-powder quantitative feeder 47 to the pulverizer 42 is quantitatively regulated. Specifically, the amount f2 of the returning powder quantitatively fed is about 3 times as high as the amount f1 of the pulverized starting material fed. That is, in this method, the classified coarse powder is circulated several times thorough the closed circuit, and there is a problem that the amount of the product obtained is small as compared with the amount of the material pulverized by the pulverizer. Accordingly, the efficiency of energy for pulverization is not sufficient. For obtaining a pulverized product having a stable particle diameter, it is necessary to always regulate the revolution number r1 of a rotating blade in the coarse-powder classifier and the amount f1 of the pulverized starting material to be supplied, thus making manual management troublesome. On the other hand, when automatic regulation is conducted, a detector or the like should be newly arranged, and it brings an economical problem. In the conventionally proposed method, visual examination is basically always necessary, and even by regular visual examination, there is a problem that stable production of toner base powder having desired particle-size distribution and production of the toner base powder with high energy efficiency are difficult, therefore production costs are hardly sufficiently reduced.
Other known methods include a method wherein two pulverizers each utilizing, for example, a jet air stream are used, and a pulverized starting material obtained by classification of starting powder is pulverized by the first pulverizer and then the pulverized material is classified to remove coarse powder, and if necessary the classified coarse powder is mixed with the starting powder and then classified, and the classified coarse powder is pulverized by the second pulverizer, whereby toner powder with a narrow particle-size distribution is produced efficiently without fusion of the toner during production (see JP-A 63-112626, JP-A 63-112627 and JP-A 5-313414); a method of producing toner powder having a small particle diameter by using a combination of a pulverizer utilizing a jet air stream (Jet Mill or I-Mill) and a mechanical pulverizer (see JP-A 5-313414 and JP-A 9-80808); and a method wherein a toner powder pulverized with a first pulverizer is rendered spherical by surface pulverization with an collision pulverizer (see JP-A7-244399). However, any of these methods cannot produce pulverized toner powder having a predetermined particle-size distribution efficiently and stably without requiring regular visual examination, thus further improvements being expected.